This invention relates to an improvement in a process for continuous casting of copper-containing metal, or the so-called "dip-forming process" of metal casting. The dip-forming system for the continuous casting of copper-containing metal comprises supplying a body of molten copper-containing metal and passing a metal core member through the molten metal and thereby accreting and solidifying molten metal on the core member.
The dip-forming process of continuous metal casting is primarily practiced with copper or copper-containing alloys for the production of copper or copper alloy rod stock for use in the manufacture of electrical conductors and wires, including enameled magnet wire for electrical apparatus, such as the enameled wire disclosed in U.S. Pat. No. 3,161,541.
The harmful effects of a high oxygen content in either the core member or in the melt upon the casting operation and cast products thereof are well known and documented in the art of continuous dip-form casting of copper-containing metals, for example note U.S. Pat. Nos. 3,484,280; 3,060,053; 3,060,056 and 3,008,201, and U.S. Pat. No. 3,490,897 and the prior art cited therein. For instance, the presence of a high oxygen content, such as approximately 20 or more parts per million by weight of the copper-containing metal, interferes with the rapid and even heat exchange between the core member and the melt solidifying thereon which reduces the uniformity and strength of the bond between the core member and the molten metal accreted thereon. The presence of such high oxygen contents and its effects additionally produce an irregular cast body or layer and configuration. Also, a high oxygen content in the melt causes irregularities and imperfections within the mass and on the surface of the cast body of solidified melt accreted over the core member, and produces undesirable oxides, among other detractions. Moreover, these adverse consequences of a high oxygen content can progressively deteriorate the casting operation and the cast products thereof because their effects are cumulative if the core member is repeatedly recycled through the system and recast and redrawn, as is often the case. Entrained imperfections within the mass of a cast layer or impediments intermediate the cast layer and the underlying metal adversely influence the drawing or reduction rolling of the cast product into units of smaller cross-sectional dimensions and the products derived therefrom such as wire.
A high oxygen content in the dip-forming system or melt, or the copper or copper alloy rod product can result from any one or combinations of several sources including, for example, the presence of oxygen source ingredients in the supply of the copper or alloy melt, the decomposition of water or hydrocarbon contaminants entrained within the melt, or simply oxygen gas absorbed from the atmosphere of the system.